On The Block: Hands-On With The George Daniels Space Travellers' Pocket Watch (Live Pics)

When man first landed on the moon, the Omega Speedmaster might have been the astronauts' chosen watch. But British watchmaker George Daniels had other ideas. Inspired by the 1969 moon landing, Daniels created the Space Travellers' pocket watch, which he described as containing "everything you'd need on a watch if you were traveling through space." We have gone hands-on with this amazing feat of cosmic horology in anticipation of it hitting the block at Sotheby's London on Tuesday.

The Dial's Amazing Three-Dimensionality

The first think you'll notice is the symmetry of the Space Travellers' dial. On the left, under the white star, are the astrological measurements, while on the right, under the sun, are the solar measurements - and perched up top between the two is, appropriately, the equation of time. The whole thing has an amazing three-dimensionality to it - a George Daniels signature - with dials overlapping and passing under one another.

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We'll start on the right with the familiar solar measurements. The main twelve-hour dial has a large subsidiary seconds and tracks mean solar time (which is just a fancy name for the time we're used to keeping with watches and clocks). There is a break in the dial between five o'clock and eight o'clock, and you can read the gold annual calendar ring in the aperture. So on this side of the dial, you've basically got an annual calendar pocket watch with large running seconds. Impressive, but fairly straightforward.

Solar Time and Annual Calendar on the Right Side of the Dial

Now, crossing over to the left, we get into more complicated territory. The main 24-hour dial (also with large subsidiary seconds) keeps Sidereal Time, also known as "Star Time." While a normal day is measured in relation to the Earth's rotation around the sun, a Sidereal day is measured in relation to Earth's movement against the fixed stars. A Sidereal day is about 3 minutes and 56 seconds shorter than a mean solar day, and this difference (combined with a few other planetary and astrological phenomena) creates the difference between mean solar time and Sidereal time. It's this difference (+/- 15 minutes) that we are measuring with an equation of time.

Sidereal Time, Moonphase, and Age of the Moon

Also housed on the left side of the dial are a graphic moon phase window and an aperture displaying the age of the moon (how many days into the current lunar cycle we are, not the age of the actual rock). As the annual calendar tells you where the Earth sits in relation to the sun, these indicators provide other reference points for our precise location in relation to the moon and the stars.

The Space Travellers' Amazing Movement, Through the Display Back

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At this point, you might be asking yourself "And why would someone need/want these two types of time on one watch?" This combination is actually inspired by an eighteenth century method of checking a watch's accuracy. By keeping a clock precisely in concert with a benchmark star, a watchmaker could ensure daily that this clock was keeping accurate time and would test watches against it. Daniels' idea was to put both of these devices in one case and to have them running off independent trains, allowing one to be used as a calibrating device for the other.

To realize this concept, Daniels needed a mathematician to help him make the astronomical calculations. Funnily enough, he was connected with a professor at Cambridge University also by the name of Daniels. Thus this watch is sometimes called the "Daniels Squared." Professor Henry Daniels helped George Daniels set a new standard for astronomical accuracy with this piece, with a ratio of .28 seconds per day.

The Space Travellers Pocket Watch in Profile

Top to bottom, the Space Travellers' is a truly exceptional piece of watchmaking. It is staunchly traditional in appearance and inspiration, while being on the forefront of technological innovation. The first Space Travellers' sold in 1988 for 220,000 CHF and estimates place this second watch in the 400,000-600,000 GBP range, roughly equivalent to $635,000-950,000.